While still hot the pipes pass to “sizing” rolls which correct any variation in inside and outside diameters. The cross or straightening rolls next smooth and clean their surfaces while straightening the pipes or boiler tubes.
After the first trip through the welding rolls, boiler tubes and certain other high grades of pipe go back into the furnace where they are reheated. They are again put through the welding rolls to make absolutely sure of a tight weld.
After cooling, the ends of each pipe are cut off. Because of the “scarfing” of the edges and the great pressure of the rolls, it is difficult to tell where the welds occur, the thickness of the walls being practically uniform all around. Lap-welded pipe of as great as 36″ diameter has been made in this way.
Pipes in Sizing and Cross Rolls
The water-pressure test is given to all lap-welded pipe as are certain tests for tensile and torsional strengths, and for ability to flatten without breaking. In the case of boiler tubes, a piece is cut from each end of each tube, which must stand flanging or spreading “cold” and also must crush down endwise under the heavy pressure applied in the testing machine without fracture or opening of the welds.
The pipe may be “threaded” to order or shipped as it comes from the testing bench.
The Finishing End
As remarked, both butt and lap-welded pipe is regularly manufactured from wrought iron and from steel.